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LRO and LCROSS: Leading the Quest to Find Water on the Moon
Color illustration of LRO spacecraft orbiting the Moon with Earth in the background.
An artist's impression of Lunar Reconnaissance Orbiter at the Moon.

In 1994, NASA and the United States Department of Defense launched a small probe called Clementine. The probe brought back startling first pieces of evidence that water ice may exist in the polar regions on the Moon.

Color image of Clementine spacecraft.

Then in 1998, more evidence came from NASA's Lunar Prospector mission. The measurement used the presence of hydrogen as a sign of potential ice deposits. As Lunar Prospector scanned the lunar surface, its neutron counters recorded the number of neutrons moving at speeds in the middle of the range. Over the Polar Regions, the counters detected a decrease in the number of neutrons moving at mid-range speeds. This meant that many neutrons were being suddenly slowed by impacts with hydrogen, so there is probably a concentration of hydrogen or even water ice somewhere in the lunar poles.

However, the measurements could not tell whether the deposits were hydrogen or ice, nor did they have the resolution to accurately locate the deposits within the polar zones.

The Lunar Reconnaissance Orbiter (LRO), scheduled for launch no earlier than June 17, will be able to do both.

Color image of Lunar Prospector spacecraft.
Lunar Prospector

Onboard, LRO contains a wide-angle and high-resolution camera system. Known as the Lunar Reconnaissance Orbiter Camera (LROC), the camera will gradually render detailed images of both lunar poles as LRO orbits over the poles and the Moon rotates under the spacecraft. Scientists using LROC will combine the images it takes during a year in orbit to make a movie that reveals the Permanent Shadow Regions (PSRs) of the Moon, areas within the depths of certain craters that may not have seen the Sun for billions of years. These areas will be the most promising places to search for hydrogen or ice.

The Moon has very little atmosphere, and therefore is drier than any terrestrial desert. So, how could water get on the moon in the first place? Some scientists believe water vapor from past comet impacts has migrated across the lunar surface to the poles to become embedded in the soil at the bottom of these dark craters. Others believe hydrogen was also embedded in the lunar soil in these polar cold traps over time. The hydrogen comes from the sun and is carried to the moon by the solar wind, a thin gas that's continuously blowing off of the solar surface and fills the entire solar system. Most of the solar wind is hydrogen.

LRO's primary science goals include:

  • Measuring radiation between Earth and the Moon
  • Measuring the polar lighting and heat environment
  • Searching for evidence of water ice and mapping hydrogen
  • Finding possible landing sites
  • Measuring elevation and mapping permanently shadowed regions

In its quest to find water ice to use as a possible natural resource, LRO will undoubtedly pave the way for NASA's plan to return humans to the moon. In addition to searching for the presence of water ice, information gleaned from the mission will also be used to select safe landing sites, determine locations for future lunar outposts and determine radiation risks for future human presence on the Moon.

Color illustration showing the LCROSS impactor heading for a collision with the Moon.
Artist's rendition of the 4,400-pound (2,000-kilogram) Centaur upper stage rocket head toward the moon's surface near the South Pole.

Accompanying LRO on its journey to the moon will be the Lunar Crater Observation and Sensing Satellite

(LCROSS), a mission that will impact the lunar surface in its search for water ice.

The Mission Objectives of LCROSS include confirming the presence or absence of water ice in a permanently shadowed crater at the Moon's South Pole.

After launch, the LCROSS spacecraft and the Atlas V's Centaur upper stage rocket will fly by the moon and enter into an elongated orbit to position the satellite for impact. On final approach, the spacecraft and Centaur will separate. The Centaur will strike the chosen lunar crater, creating a debris plume that will rise above the surface. Four minutes later, LCROSS will fly through the debris plume, collecting and relaying data back to Earth before striking the moon's surface and creating a second debris plume. Scientists will use data from the debris clouds to determine the presence or absence of water ice.

Last Updated: 24 January 2011

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Last Updated: 24 Jan 2011